Conventionally, in a device that is mounted in a vehicle such as automobile and is configured to predict an approach between vehicles, a GPS is used to detect positions of the vehicles. A display device displays a road map and positions of a driver's vehicle and an opponent vehicle. A future approach between these vehicles is predicted using the road map, the positions of the vehicles, and so on.
Japanese Laid-Open Patent Application Publication No. 2002-140800 discloses an information provision apparatus for a motorcycle that emits an alarm to a driver depending on a road condition and a driving state of the vehicles. The alarm is displayed on a display device in the form of an alarm mark or numeric or alphabetical characters.
In the device configured to predict the approach between the vehicles, since the approach between the vehicles is predicted using the information of the road map displayed on the display device, the display device is required to have a screen of a substantial size to display a precise image such as a road map image, and it is thus difficult to reduce the size of the display device. To predict the approach between the vehicles using the information of the road map, data processing such as conversion of a position of a road on the map into a coordinate system identical to a coordinate system representing the position of the vehicle is needed. As a result, a tremendous volume of data is required to be processed.
In the device disclosed in Japanese Laid-Open Patent Application Publication No. 2002-140800, the alarm mark indicates messages stating that there is a crossing vehicle or there is a vehicle coming from the opposite direction. Since the alarm mark is displayed to overlap with a map and so on of a navigation device, its impact may be weak to the driver. The driver is unable to easily recognize a velocity of the opponent vehicle or a distance from the opponent vehicle from the alarm mark. In addition, since the alarm mark is displayed to overlap with the map and so on as described above, it is difficult to reduce the size of the display device.